Chair provided with a backrest

ABSTRACT

A chair with a backrest is arranged so that the seat can be shifted forwardly to a rest position upon a rearward inclination of the backrest. The front end of the seat is supported pivotably on a support base, and the seat is movable forwardly and rearwardly. A balancing member is provided below the seat, and the support base supports a fulcrum of the balancing member set between a front and rear point of action of the balancing member. A backrest is provided on the rear end of the balancing member, and a rear part of the seat is supported on the rear point of action of the balancing member through seat receiving means. An upward movement of the front point of action of the balancing member is translated by motion translating means to a forward movement of the seat.

TECHNICAL FIELD

This invention relates to a chair provided with a backrest in which aseat can be shifted forwardly into a rest position by rearwardinclination of the backrest.

BACKGROUND ART

In many chairs with a backrest as well as chairs for office work, thebackrest can be inclined rearwardly. There is known a chair of this typeso constructed that a backrest is mounted inclinably on a support basesupporting a seat, with a resiliently urging mechanism resilientlyurging the backrest forwardly. There is also known another chair soconstructed that a seat and a backrest form an integral body and thefront end of the seat is supported inclinably on the front end of asupport base, with a resiliently urging mechanism resiliently urging theseat and the backrest in a required direction.

In these chairs, when a rearwardly directed pressure is applied to thebackrest, only the backrest or both the backrest and the seat arerearwardly inclined against the urging force of the above-mentionedresiliently urging mechanism, so that the chair can take a restposition.

With this arrangement, however, there is a problem that when thebackrest is inclined rearwardly, the center of gravity of the user isgreatly shifted rearwardly relative to a support base provided on a leg,so that the user is likely to fall down rearwardly.

On the other hand, there are known chairs in which the seat can beshifted forwardly when the backrest is inclined rearwardly. Among suchchairs are chairs used for buses and trains, in which the seat issupported on a support base slidably in forward and rearward directions,and the lower end of the frame of the backrest is mounted pivotally onthe rear end of the above-mentioned seat, and the intermediate portionof the backrest frame is mounted on the above-mentioned support basepivotally or both pivotally and slidably up and down.

In this type of chair, when the backrest is inclined, the position ofthe occupant is not greatly shifted rearwardly. With this arrangement,however, unless the relatively upper portion of the backrest is pushedrearwardly, the backrest cannot be pivoted. This poses a problem thatwhen the user pushes the backrest with his whole back to take a restposition, the movement of his back does not coincide with that of thebackrest, so that he feels uncomfortable.

This invention has been proposed in view of these problems encounteredin the prior art, and its object is to provide a chair having abackrest, in which the seat is shifted forwardly upon rearwardinclination of the backrest, thereby to prevent the chair from fallingdown rearwardly, and in which the backrest can be inclined rearwardly bypushing any part of the backrest rearwardly without causinguncomfortable feeling to the occupant pushing the backrest.

DISCLOSURE OF THE INVENTION

To attain the above-mentioned object the invention has adopted thefollowing construction.

The chair with a backrest constructed in accordance with the inventionis characterized by the provision of a support base, a seat having afront end supported on the support base movably in forward and rearwarddirections, a balancing member positioned below the seat so as to extendlongitudinally and having a fulcrum supported on the above-mentionedsupport base, a backrest provided on the rear part of the balancingmember, seat receiving means for connecting the rear end of theabove-mentioned seat to a portion of the above-mentioned balancingmember at the rear side of the fulcrum so as to be movable forwardly andrearwardly, and motion translating means for translating an upwardmovement of the front end of the above-mentioned balancing member to aforward movement of the above-mentioned seat.

With this arrangement, as the user operates to push the backrest withhis back rearwardly from a reference position in which the backreststands upright and the seat is retained at the most retreated positionthereof, the balancing member with the backrest is pivoted rearwardlyabout the fulcrum thereof. As a result, the front point of action of thebalancing member is moved upwardly, and this upward movement istransmitted to the above-mentioned seat by the motion translating means,so that the seat is shifted forwardly, with its rear end descending. Atthis time, because the above-mentioned backrest is pivoted rearwardly onthe fulcrum of the balancing member positioned below the above-mentionedseat, the whole backrest is inclined rearwardly and simultaneouslyshifted rearwardly. Therefore, the movement of the user's back acting onthe backrest properly coincides with the movement of the backrest, sothat the user never feels uncomfortable. As the backrest is bothinclined and shifted rearwardly, the seat advances forwardly, and thecenter of gravity is not greatly shifted rearwardly. This can eliminatethe disadvantage that when a rest position is taken, the chair is likelyto fall down rearwardly.

Moreover, since the rear end of the seat is supported on the rear pointof action of the balancing member through the seat receiving means, therearward pivotal movement of the balancing member can effectively beused to effect a descending motion of the rear end of the seat, so thatthere is no need for using complex mechanisms to effect the descendingmotion of the seat.

If the chair is so constructed that the rear end of the seat may descendrelative to the front end thereof upon forward movement of the seatcaused by rearward inclination of the backrest and the upward movementof the front end of the balancing member, it is possible to eliminatethe feeling of forward sliding the user would otherwise have when he istaking a rest position.

In accordance with the invention, the chair with a backrest having theabove-mentioned basic arrangement is provided with a resiliently urgingmechanism for resiliently urging the seat rearwardly.

With this arrangement, when the backrest is inclined rearwardly and theseat is moved forwardly from the above-mentioned reference position, theurging force applied by the above-mentioned resiliently urging mechanismfunctions as a resistive force against the movement of the seat.Therefore, the user must push the backrest rearwardly against theresilient repellent force in order to take a rest position. When theuser raises the upper half of his body or leaves the chair, the seat isreturned to its most retreated position by the urging force of theabove-mentioned resiliently urging mechanism, and at the same time thebalancing member is pivoted forwardly and the backrest stands upright,so that the whole chair is returned to its reference position by itself.

The invention employs as the seat receiving means the means which canproduce a force for pulling the above-mentioned seat rearwardly byutilizing a force downwardly acting on the seat.

With this arrangement, the following operations and effects are added tothe chair. With the seat receiving means of this construction, arearward pulling force corresponding to the weight of the user seated inthe chair acts on the seat. The pulling force acts on the front point ofaction of the above-mentioned balancing member as a downwardly directedforce through the motion translating mechanism. On the other hand, adownwardly directed force corresponding to the weight of the user actson the rear point of action of the balancing member. Therefore, only ifthe position of the fulcrum and the dimension of each component part arepreset so that a downwardly directed force, which varies with the user'sweight, remains on the front point of action even after theabove-mentioned downwardly directed force acting on the front point ofaction has been offset by the above-mentioned downwardly directed forceacting on the rear point of action, the above-mentioned balancing memberis likely to be pivoted forwardly by a force corresponding to theweight. Therefore, the user of a heavy weight must exert a large forceto incline the backrest rearwardly, while a smaller force suffices withthe user of a light weight. The backrest is inclined rearwardly bydirectly pushing it with one's back. Since a person of a heavy weightusually provides by his back a larger operating force on the backrestthan a person of a light weight, it is preferable to have the force foroperating the backrest variable in the above-mentioned manner.

The invention further includes the following concrete arrangements. Theseat receiving means may be provided with link members each having alower end pivotally connected to the above-mentioned balancing memberand an upper end pivotally connected to the above-mentioned seat, and soarranged that at the reference position where the seat is maintained atits most retreated position, the upper pivot end of each link member ispositioned rearwardly of the lower pivot end thereof.

With this arrangement, the above-mentioned operation, wherein at aninitial stage the backrest begins to incline from the above-mentionedreference position, and a person having a greater weight must exert alarger force for operating the backrest by his back, can be effected bya simple construction with a few component parts.

The improved chair with a backrest of the invention is provided with alocking mechanism for stopping the movement of the above-mentioned seatand backrest at a desired position.

With this arrangement, the backrest and the seat can be lockedsimultaneously at any desired position by a proper operation by theuser, so that the user may relax himself and take a comfortable restposition on the chair.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of one embodiment of the invention, with partthereof being omitted;

FIG. 2 is a side view of the same embodiment with the backrest at aninclined position;

FIG. 3 is a side view of the main portion of the same embodiment;

FIG. 4 is a view as viewed in the direction of the arrow A in FIG. 3;

FIG. 5 is an enlarged side view of the main portion of the sameembodiment;

FIG. 6 is a perspective view of a portion of the resiliently urgingmeans, as shown disassembled;

FIG. 7 is a perspective view of the main portion, as shown disassembled;

FIGS. 8 and 9 are side views of the same embodiment corresponding toFIG. 3 for explanation of the operation of the same embodiment;

FIGS. 10 and 11 are schematic side views of different embodiments,respectively, wherein the balancing member has different supportingstructures;

FIGS. 12, 13 and 14 are schematic side views of different embodiments,respectively, with different forms of the motion translating means;

FIGS. 15, 16 and 17 are schematic side views of different embodiments,respectively, with different forms of the seat receiving means;

FIG. 18 is a schematic side view of another embodiment, wherein thebalancing member is supported at a different position;

FIG. 19 is a schematic side view of another embodiment, with a lockingmechanism added thereto;

FIG. 20 is an enlarged sectional view taken alone line B--B in FIG. 19;and

FIG. 21 is a schematic side view of another embodiment with a modifiedlocking mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1 through 9, one embodiment of the invention willbe described below.

As shown in FIGS. 1 and 2, the chair with a backrest comprises a supportbase 2 mounted on a leg 1, a seat 3 having a front end 31 supported onthe support base 2 so as to be movable forwardly and rearwardly, abalancing member 4 positioned below the seat 3 so as to extendlengthwise thereof and having a fulcrum 43 supported on theabove-mentioned support base 2 between a rear and a front point ofaction 41 and 42, a backrest 5 provided on the rear end 44 of thebalancing member 4, seat receiving means 6 for connecting the rear end32 of the above-mentioned seat 3 to the above-mentioned rear point ofaction 41 of the above-mentioned balancing member 4 so as to be movableforwardly and rearwardly, and motion translating means 7 for translatingan upward movement of the above-mentioned front point of action 42 ofthe above-mentioned balancing member 4 to a forward movement of theabove-mentioned front point of action 42 of the above-mentioned seat 3.

As shown in FIGS. 3 through 5, the support base 2 is a channel membercomprising a bottom plate 21 fixed to the upper end of theabove-mentioned leg 1 and a pair of side plates 22 standing integrallyon the opposite lateral edges of the bottom plate 21. The front end 31of the above-mentioned seat 3 is supported on the side plates 22 closeto the front ends thereof by a pair of front link members 8. A seatreceiving cover 23 is provided on the bottom of the support base 2.

As shown in FIG. 1, the seat 3 is composed of an inner shell not shownbut mounted on a receiving frame 33, a cushion not shown but disposed onthe inner shell, and a surface finishing material 34 covering the outersurface of the cushion. The under surface of the above-mentioned innershell is covered with an outer shell 35. The central portion of theouter shell 35 has an opening to prevent interference with theabove-mentioned seat receiving cover 23. As shown in FIGS. 3, 5 and 7,the above-mentioned receiving frame 33 is provided with a top plate 36for supporting the above-mentioned inner shell, and a pair of sideplates 37 depending integrally from the opposite lateral edges of thetop plate 36. The upper pivot ends 81 of the above-mentioned front linkmembers 8 are pivoted by a shaft 82 to the side plates 37 close to theirfront ends, and the lower pivot ends 83 of the front link members 8 arepivoted by a shaft 84 on the side plate 22 of the above-mentionedsupport base 2. At the reference position where the seat 3 is retainedat the most retreated position (refer to the real lines in FIGS. 1 and3), the upper pivot ends 81 of the above-mentioned front link members 8are so arranged as to be positioned rearwardly of the lower pivot ends83 thereof.

As shown in FIGS. 3, 4 and 7, the balancing member 4 comprises a pair ofparallel plates 45 extending lengthwise and a connecting plate 46integrally connecting the rear end portions of the parallel plates 45.The fulcrum 43 provided at the middle point of the above-mentionedparallel plates 45 is pivotally supported by a shaft 47 on bosses 24provided on the side plates 22 of the above-mentioned support base 2.The backrest 5 is connected to the rear end 44 of the balancing member4.

As shown in FIG. 1, the backrest 5 comprises a frame 51 secured to therear end of the above-mentioned balancing member 4, an inner shell notshown but secured to the frame 51 by a channel member 52, a cushion notshown but attached to the front surface of the inner shell and a surfacefinishing material 53 covering the outer surface of the cushion. Anouter shell 54 covers the above-mentioned inner shell, theabove-mentioned frame 51 and the channel member 52 at the rear surfacesthereof. The inner shell, the cushion, the surface finishing material 53and the outer shell 54 of the backrest 5 of this embodiment are madeintegral with the inner shell, the cushion, the surface finishingmaterial 34 and the outer shell 35 of the above-mentioned seat 3,respectively. However, they may be made separate from each other.

The seat receiving means 6 is so constructed as to utilize thedownwardly directed force acting on the above-mentioned seat 3 toproduce a force pulling the seat 3 rearwardly. In particular, as shownin FIGS. 3 through 5, the above-mentioned seat receiving means 6 isprovided with a pair of rear link members 65 each having an upper pivotend 61 pivoted by a shaft 62 to the above-mentioned receiving frame 33and a lower pivot end 63 pivoted by a shaft 64 to the above-mentionedbalancing member 4. At the reference position where the above-mentionedseat 3 is retained at the most retreated position, the upper pivot ends61 of the above-mentioned link members 65 are positioned rearwardly ofthe lower pivot ends 63 thereof.

As shown in FIGS. 3 through 5 and FIG. 7, the motion translating means 7comprises a slot 71 formed in the above-mentioned balancing member 4close to each front point of action 42 thereof so as to extendlengthwise, an arm 72 integral with and projecting from each front linkmember 8, and a connecting pin 73 projecting from each arm 72 so as toslidably engage the slot 71. The line extending from the axis of theabove-mentioned lower pivot end 83 of each front link member 8 to theaxis of the upper pivot end 81 thereof is so arranged as to cross theline extending from the axis of the lower pivot end 83 to the axis ofthe above-mentioned connecting pin 73 at approximately right anglestherewith.

In the above-mentioned chair there is also provided resiliently urgingmeans 9 between the above-mentioned support base 2 and theabove-mentioned seat 3. The resiliently urging means 9 comprises a mainspring 91 and a pair of subsidiary springs 92. The main spring 91 is atension coil spring extending between the above-mentioned shaft 82supported by the receiving frame 33 of the above-mentioned seat 3 and across bar 93 supported by the rear portion of the above-mentionedsupport base 2. Each subsidiary spring 92 comprises a helical torsionspring wound around the above-mentioned shaft 84 supported on theabove-mentioned support base 2. The front end 94 of each subsidiaryspring 92 is engaged by the above-mentioned support base 2 through aspring-force regulating mechanism 10 while the rear end 95 thereof isresiliently engaged by the above-mentioned shaft 82. As shown in FIGS. 5and 6, the spring-force regulating mechanism 10 comprises a flangedbearing sleeve 101 fitted in a hole 25 formed in the front end portionof the bottom plate 21 of the above-mentioned support base 2, a controlgrip 103 having a stem 102 rotatably inserted through the bearing sleeve101, a feed screw 104 integral with the stem 102 of the control grip103, and a retainer 105 fitted to the screw 104. The retainer 105, forexample, can be a shaft-like member crossing the above-mentioned screw104 at right angles therewith, and provided near the opposite endsthereof with a pair of annular recesses 106 which the front ends 94 ofthe subsidiary springs 92 engage. A retainer ring 107 is provided aboutthe stem 102 of the above-mentioned control grip 103 so as to besupported on the flange of the above-mentioned bearing sleeve 101 via athrust bearing 108.

The operation of the chair will now be described.

In the reference position shown in real lines in FIGS. 1 and 3, thebackrest 5 stands upright, and the seat 3 is kept at the most retreatedposition thereof. This reference position is set to the most suitableone for office work. As the user pushes with his back theabove-mentioned backrest 5 rearwardly from the reference position, thebalancing member 4 together with the backrest 5 is pivoted rearwardlyabout the fulcrum 43. As a result, the front point of action 42 of thebalancing member 4 is upwardly moved and the upward movement istransmitted to the above-mentioned seat 3, which moves forwardly withthe rear end 32 thereof descending. In particular, as the front point ofaction 42 of the above-mentioned balancing member 4 is moved upwardly,each front link member 8 connected to the front point of action 42 bythe connecting pin 73 of the arm 72 is forwardly pivoted about the lowerpivot end 83 so that the upper pivot end 81 shifts the seat 3 forwardly.At the same time each rear link member 65 is also pivoted forwardlyabout the lower pivot end 63, which is supported on the rear point ofaction 41 of the above-mentioned balancing member 4. Therefore, providedthat the dimensions of the component parts are so predetermined, as inthe present embodiment, that the degree of downward movement of eachrear link member 65 as a whole caused by the pivotal movement of theabove-mentioned balancing member 4 is greater than that of upwardmovement of the upper pivot end 61 of each rear link member 65 caused bythe pivotal movement of the rear link member 65, the above-mentionedseat 3 is caused to advance while descending at the rear end 32 thereof.As a result, the chair can be shifted to a rest position (as shown indot-and-dash lines in FIGS. 2 and 3 and FIG. 9) without giving the usera feeling of slipping forwardly. Moreover, with this arrangement, bymaking the best use of the rearward pivotal movement of the balancingmember 4 it is possible to make the rear end 32 of the above-mentionedseat 3 descend without the necessity of using any complex mechanism fordescending motion. Therefore, it is easy to manufacture the chair.

As mentioned above, as the seat 3 advances, the above-mentioned backrest5 is pivoted rearwardly about the fulcrum 43 of the balancing member 4disposed below the seat 3, so that the whole backrest 5 is shiftedrearwardly while being inclined rearwardly. Therefore, the motion of theuser's back acting on the backrest 5 properly coincides with themovement of the chair back 5, so that the user does not feeluncomfortable. When the backrest 5 is shifted rearwardly while beinginclined rearwardly, the seat 3 advances, so that it is possible toprevent occurrence of a troublesome condition that the center of gravityof the user is shifted rearwardly thereby to cause the chair to falldown rearwardly.

The chair is provided with resiliently urging means 9 for resilientlyurging the above-mentioned seat 3 rearwardly. With this arrangement,when the backrest 5 is inclined rearwardly from the above-mentionedreference position thereby to advance the seat 3, the urging force ofthe above-mentioned resiliently urging means 9 counteracts the movementthereof. Therefore, the user pushes the backrest 5 rearwardly againstthe resilient force so as to take a rest position. Then, when theabove-mentioned user raises the upper half of his body on the chair orleaves the chair, the above-mentioned seat 3 is returned to its mostretreated position by the resilient force of the above-mentionedresiliently urging means 9, and the balancing member 4 is shiftedforwardly, and the backrest 5 stands upright, so that the whole chair isreturned to its reference position by itself. In this referenceposition, since the frame 51 of the backrest 5 abuts on and is retainedby a stopper not shown, the backrest 5 is not pivoted further forwardly.

Moreover, with the above-mentioned arrangement of the seat receivingmeans 6, a backward pulling force corresponding to the weight of theuser seated in the chair acts on the seat 3. In particular, when thechair is positioned at the reference position close thereto, the rearlink members 65 constituting the seat receiving means 6 are inclinedrearwardly. Under the condition, if a downward force corresponding tothe weight of the user acts on the upper pivot ends 61 of the rear linkmembers 65 through the seat 3, the rear link members 65 are shiftedrearwardly. As a result, a rearward pulling force is applied to thereceiving frame 33 of the seat 3 connected to the upper pivot ends 61 ofthe rear link members 65. This pulling force acts as a downward force onthe front point of action 42 of the above-mentioned balancing member 4through the motion translating means 7. In particular, as theabove-mentioned receiving frame 33 is pulled rearwardly, a force actingon the front link members 8 to cause them to pivot rearwardly is appliedto the front link members 8 having their upper pivot ends 81 connectedto the receiving frame 33. As a result, the arm 72 provided on eachfront link member 8 is pivoted downwardly, and the connecting pin 73projecting from each arm 72 pushes the front point of action 42 of theabove-mentioned balancing member 4 downwardly. An additional downwardforce caused by the weight of the user acts on the upper pivot ends 81of the front link members 8 through the seat 3. This downward force alsoacts as a force to pivot the front link members 8 rearwardly, andfunctions as a force to push the front point of action 42 of theabove-mentioned balancing member 4 downwardly through theabove-mentioned connecting pins 73. Thus, a downward force increasing ordecreasing depending upon the weight of the user (which force will bereferred to as "the weight-depending front force" for abbreviationhereinafter) is applied to the front point of action 42 of theabove-mentioned balancing member 4. On the other hand, a downward forceincreasing or decreasing depending upon the weight of the user (whichforce will be referred to as "the weight-depending rear force" forabbreviation hereinafter) is applied to the rear point of action 41 ofthe balancing member 4 through the rear link members 65. In thisembodiment, the arrangement is such that the weight-depending rear forceacting on the rear point of action 41 cannot offset the weight-dependingfront force acting on the front point of action 42. In other words, theposition of the fulcrum 43 and the dimensions of the component membersare preset so that the previously mentioned downward force increasing ordecreasing depending upon the weight of the user remains on the frontpoint of action 42. As a result, the above-mentioned balancing member 4and backrest 5 are pivoted forwardly by a force corresponding to theweight. Therefore, a user of a heavy weight must exert a large force toincline the backrest rearwardly, while a user of a light weight needsonly a smaller force.

The backrest 5 is inclined rearwardly by a user directly pushing it withhis back. Usually, a person of a heavy weight has a larger force than aperson of a light weight to push the backrest with his back. Therefore,it is preferable that the force for operating the backrest should varyin the above-mentioned manner. If chairs for use in meeting rooms orwith office automation equipment, that is, chairs to be used commonly bypersons of different physiques have such functions as mentioned above,the initial repellent strength of the backrest 5 need not be adjusted todifferent users, so that the chair can be used conveniently.

The above-mentioned operation is conducted at the initial stage wherethe backrest 5 begins to be inclined rearwardly from the above-mentionedreference position. In particular, as the rearward inclination of thebackrest 5 increases so that the front link members rise upright, theabove-mentioned weight-depending front force acting on the front pointof action 42 of the balancing member 4 gradually decreases. On the otherhand, the above-mentioned weight-depending rear force acting on the rearpoint of action 41 of the balancing member 4 does not greatly change inspite of the change in inclination of the front link members 8.Therefore, the priority of the weight-depending front force disappearswell before the link members 8 and 65 stand upright as shown in FIG. 8,so that the repellent force of the backrest 5 no longer increases ordecreases depending upon the weight of the user.

As described above, the above-mentioned seat 3 is resiliently urgedrearwardly by the main spring 91 and the subsidiary springs 92.Therefore, this resilient urging force function as a downward force(which will be referred to as "the spring-depending force" forabbreviation hereinafter) on the front point of action 42 of theabove-mentioned balancing member 4 through the the front link members 8.The spring-depending force increases as the seat 3 advances to increasethe amount of resilient deformation of the springs 91 and 92. After theabove-mentioned backrest 5 has been greatly inclined rearwardly, so thatthe weight-depending force to urge the backrest 5 forwardly has lost itseffect, the spring-depending force only urges the backrest 5 forwardly.The spring-depending force is produced by the pulling force of the mainspring 91 and the pressing force of the subsidiary springs 92.Therefore, by adjusting the spring force of the above-mentionedsubsidiary springs 92 it is possible to change the spring-dependingforce thereby to change the magnitude of the force to urge the backrest5 forwardly. If a single spring corresponding to the above-mentionedmain spring 91 was provided to urge the seat 3 rearwardly, a complicatedmechanism would be required to adjust the spring force from outside. Onthe contrary, since the chair of the invention is so arranged that theseat 3 is urged rearwardly by the main spring 91 and the subsidiarysprings 92, and the subsidiary springs 92 are provided at the forwardend of the support base 2, it is possible to adjust the spring force ofthe springs from outside by using the above-mentioned simplespring-adjusting mechanism 10. With this arrangement, it is alsopossible to arrange so that at the initial stage of inclination of thebackrest 5 the subsidiary springs 92 do not work, and that when theweight-depending force has stopped urging the backrest 5 forwardly, thesubsidiary springs 92 become active.

In the above-mentioned embodiment, the main spring is of such a typethat the spring force increases linearly as it expands. The spring mayalso be of such a type that as the spring expands, the spring forceincreases curvilinearly with its rate of change increasing. As anexample of the spring having such a characteristic there is available acoil spring which has a high coil density in the opposite ends and a lowcoil density in the middle thereof.

Examples of the mode of supporting the balancing member are shown inFIGS. 10 and 11.

The balancing member 204 shown in FIG. 10 has a pair of slots 248 in itsfulcrum 243. The balancing member 204 is swingably supported by a shaft247 fixed to the support base 202 and engaging the slot 248. In thiscase, a pivoting mechanism can be provided in not only the connectionbetween each rear link member 265 and the balancing member 204 but alsothe connection between each front link member 208 and the balancingmember 204. In FIG. 10, 201 is a leg, 203 is a seat, and 205 is abackrest.

The balancing member 304 shown in FIG. 11 has its fulcrum 343 pivoted tothe lower end of a pair of central link members 348. The upper end ofeach central link member 348 is pivoted to the support base 302. Withthis arrangement, it is possible to provide a pivoting mechanism in allof the fulcrum 343 of the balancing member 304, the connection betweeneach rear link member 365 and the rear point of action 341, and theconnection between each front link member 308 and the front point ofaction 342. Because the pivoting mechanism always makes it possible tohave the outer surface of the pivot shaft in contact with or close tothe inner surface of the hole for receiving the shaft, it caneffectively prevent foreign bodies from entering between the surfacesthereby to avoid or suppress increase of the sliding resistancetherebetween and production of screeching sounds for a long time. Sincechairs are usually used for a long period of time without particularmaintenance work, it is advantageous that all connecting portions ofmovable parts include a pivoting mechanism. In FIG. 11, 301 is a leg,303 is a seat, and 305 is a backrest.

Besides the motion translating means described above, those shown, forexample, in FIGS. 12 through 14 can also be used.

In the motion translating means 407 shown in FIG. 12, a pin 473 is fixedto the front point of action 442 of the balancing member 404, and thepin 473 is in sliding contact with the lower edge of the arm 472 of eachfront link member 408. In FIG. 12, 401 is a leg, 402 is a support base,403 is a seat, 405 is a backrest, and 443 is a fulcrum.

In the motion translating means 507 shown in FIG. 13 a pin 573 is fixedto the front point of action 542 of the balancing member 504, and thepin 573 is in sliding contact with the rear edge of each front linkmember 508 inclined rearwardly. In FIG. 13, 501 is a leg, 502 is a seat,505 is a backrest, and 543 is a fulcrum.

In the motion translating means 607 shown in FIG. 14 those teeth 674 and675 which form part of a gear are formed on the front point of action642 of the balancing member 604 and the forward end of the arm 672 ofeach front link member 608, respectively, and these teeth 674 and 675mesh with each other. In FIG. 14, 601 is a leg, 602 is a support base,603 is a seat, 605 is a backrest, and 643 is a fulcrum.

Besides the seat receiving means described above, those shown, forexample, in FIGS. 15, 16 and 17 can be used.

In the seat receiving means 706 shown in FIG. 15 a pair of projections748 are provided on the rear point of action 741 of the balancing member704, and a pin 749 projecting from each projection 748 slidably engageseach slot 738 formed in the receiving frame 733 of the above-mentionedseat 703. In FIG. 15, 701 is a leg, 702 is a support base, 705 is abackrest, and 743 is a fulcrum.

In the seat receiving means 806 shown in FIG. 16, a pivotable frame 861is arranged below the receiving frame 833 of the seat 803 with the frontend thereof pivotally supported on the support base 802, and the rearend of the pivotable frame 861 is supported on the rear point of action841 of the balancing member 804 through each link member 865, with a pin862 standing near the rear end of the frame 861 and slidably engagingeach slot 838 formed in the above-mentioned receiving frame 833. In thisembodiment, a pair of slots 839 is also provided near the front end ofthe above-mentioned receiving frame 833, and a pin 863 projecting fromthe front end of the above-mentioned support base 802 slidably engageseach slot 839 thereby to support the front end of the seat 803 on theabove-mentioned support base 802. A vertically extending, rearwardlyinclined slot 871 is provided in each side plate of the above-mentionedreceiving frame 833, and a pin 881 projecting from the upper end of eachfront link member 808 slidably engages the slot 871. A connecting pin873 projects from the arm 872 of each front link member 808, andslidably engages each slot 871 formed at the front point of action 842in the balancing member 804. With this arrangement, as the front pointof action 842 of the balancing member 804 is shifted upwardly uponrearward inclination of the backrest 805, each front link member 808 ispivoted forwardly so as to shift the receiving frame 833 forwardly. Whenthe receiving frame 833 advances forwardly, the frame 833 graduallyrises by the pins 862, 863 guided by the slots 838, 839. However, sincethe above-mentioned pivotable frame 861 has its rear end connected tothe rear point of action 841 of the balancing member 804, the rear pin862 descends with forward movement of the receiving frame 833.Therefore, when the chair is observed as a whole, as the backrest 805 isinclined rearwardly and the seat 803 advances, the rear end of the seat803 descends properly. The slots 838 and 839 may extend horizontally orslightly aslant forwardly.

The seat receiving means 906 shown in FIG. 17 is provided with a pair ofrear link members 965 of a different length from the front link members908. In FIG. 17, 901 designates a leg, 902 designates a support base,905 designates a backrest, and 943 designates a fulcrum.

FIG. 18 shows another embodiment in which the fulcrum 1043 of thebalancing member 1004 is set at a relatively forward position. In thedrawing, 1001 is a support base, 1003 is a seat, 1005 is a backrest.

FIGS. 19 and 20 show an embodiment in which locking means 1108 isprovided between the support base 1102 and the balancing member 1104.The locking means 1108 is constructed by alternately piling up aplurality of friction plates 1182 each having a vertically extendingslot 1181 and a leaf spring 1184 having a vertically extending slot 1183with a spacer 1185 interposed therebetween, and fastening the upper endsof these friction plates 1182, the upper end of the above-mentioned leafspring 1184 and the above-mentioned spacers 1185 to the boss 1121 of thesupport base 1102 by means of a fastening shaft 1186. A pin 1141provided on the balancing member 1104 slidably engages theabove-mentioned slots 1181 and 1183, and a plurality of pad members 1187mounted on the pin 1141 are interposed between the balancing member 1104and the above-mentioned friction plates 1182, between adjacent twofriction plates 1182, and between the friction plates 1182 and the leafspring 1184. A wire 1183 is connected to the lower end of the leafspring 1184 for pulling it outwardly. By handling an operating lever notshown but provided below the seat 1103 the wire 1183 can be pulled. Withthis arrangement, when no pulling force is exerted on the wire 1188, theresilient force of the leaf spring 1184 presses the pad members 1187,the friction plates 1182 and the leaf spring 1184 against each other. Asa result, the movement of the balancing member 1104 is braked by thefrictional force produced at the pressed areas between the members, sothat the seat 1103 and the backrest 1105 are locked. When the wire 1188is pulled by operating the control lever, the above-mentioned leafspring 1184 is outwardly curved thereby to release the pressed conditionof the pad members 1187 and the friction plates 1182. As a result, thebalancing member 1104 can be pivoted, and the above-mentioned lockedcondition of the seat 1103 and the backrest 1105 is released.

FIG. 21 shows another embodiment of the locking means. This lockingmeans 1208 comprises a gas spring 1281 of a construction similar to thegas spring used for adjusting the length of the legs of a chair andinterposed between the support base 1202 and the seat 1203. Inparticular, the gas spring 1281 which extends by the repelling force ofa gas enclosed therein is provided between a cross member 1221 mountedon the above-mentioned support base 1202 and a shaft 1231 mounted on therear end of the seat 1203. As is well known, the gas spring 1281 hasbuilt therein a valve mechanism for stopping flow of the interior fluidand locking the extension of the spring, it being possible to open andclose the valve mechanism from outside. In this embodiment the valvemechanism can be controlled by a control lever not shown but providedbelow the seat 1203. In FIG. 21, 1201 is a leg, 1204 is a balancingmember, and 1205 is a backrest. With this arrangement, if the valvemechanism of the gas spring 1281 is kept at a closed position thereby toprevent free extension or contraction of the gas spring 1281, the seat1203 cannot freely move forwardly or rearwardly, so that inclination ofthe backrest 1205 is restricted. When the valve mechanism is opened byoperating the control lever, the gas spring 1281 performs its springfunction to resiliently urge the seat 1203 rearwardly. Then, when theuser pushes the backrest 1205 rearwardly against the resilient force,the seat can be shifted to its rest position. Thus, the gas spring 1281of this embodiment also functions as resiliently urging means.

Several embodiments of the invention having been described above, theinvention is not limited thereto, but there may be various modificationswithout departing from the scope of the invention.

As mentioned above, the chair with a backrest constructed in accordancewith the invention is suitable for use as a chair in a meeting room, foroffice work, or a chair an operator of an OA instrument uses. Theinvention can also be applied to a chair without a leg.

What is claimed is:
 1. A chair which comprises:a support base; a seat which is movable forwardly and rearwardly, said seat comprising a front part and a rear part, wherein the front part is pivotably supported by the support base; a balancing member positioned below the seat so as to extend longitudinally, said balancing member having a front portion, a rear portion, and a fulcrum set between the front portion and the rear portion so that said front portion is movable upwardly and downwardly, said balancing member being supported by said support base at the fulcrum; a backrest provided on the rear portion of the balancing member; seat receiving means for pivotally connecting the rear part of said seat to the rear portion of said balancing member; and motion translating means for operably connecting the front portion of said balancing member to the front part of said seat, said motion translating means translating an upward movement of said front portion of said balancing member to a forward movement of said seat.
 2. The chair according to claim 1, wherein as said seat advances upon an upward movement of said front portion of said balancing member caused by a rearward inclination of said backrest, the rear part of said seat can descend relative to the front part of the seat.
 3. The chair according to claim 1, further including resiliently urging means between the support base and the seat for resiliently urging said seat rearwardly.
 4. The chair according to claim 1, wherein said seat receiving means includes means for pulling the seat rearwardly in reaction to a downward force on the seat exerted by a user of the chair.
 5. The chair according to claim 4, wherein said seat receiving means is provided with link members each having a lower pivot end pivoted to said balancing member and an upper pivot end pivoted to said seat; and wherein at the reference position where said seat is maintained at its most retreated position, said upper pivot ends of each said link member is positioned rearwardly of said lower pivot end.
 6. The chair according to claim 1, further including locking means connected to the support base and the balancing member for stopping the movement of said seat and said backrest at a desired position.
 7. The chair according to claim 1, wherein the front part of the seat is supported on the support base by front link members each having a lower pivot end pivoted to said support base and an upper pivot end pivoted to said front part of the seat, and wherein at the reference position where said seat is maintained at its most retreated position, said upper pivot end of each said link member is positioned rearwardly of said lower pivot end.
 8. The chair according to claim 7, wherein the motion translating means comprises a slot formed in the front portion of the balancing member and extending lengthwise, an arm integral with the front link member, and a connecting pin projecting from said arm so as to slidingly engage said slot.
 9. The chair according to claim 7, wherein the motion translating means comprises a pin fixed to the front portion of the balancing member, and an arm integral with the front link member, said pin being in sliding contact with the lower edge of said arm.
 10. The chair according to claim 7, wherein the motion translating means comprises teeth in the front portion of the balancing member, and teeth in an arm integral with the front link member, such that the teeth in the balancing member and the teeth in the arm mesh with each other.
 11. The chair according to claim 1, wherein the seat receiving means comprises a lengthwise slot in the seat, a projection arm on the rear portion of the balancing member, and a pin extending from said projection arm, wherein said pin slidably engages said slot.
 12. The chair according to claim 1, wherein the balancing member comprises a pair of parallel plates extending longitudinally and a connecting plate integrally connecting the rear portions of said parallel plates. 